Electronic control for gravimetric feeders



Sept. 9, 1952 G. KAST 2,609,965

ELECTRONIC CONTROL FOR GRAVIMEZTRIC FEEDERS Filed Nov. 30, 1949 Jo 3 V INVENTOR.

Patented Sept. 9, 1952 UNITED STATES PATENT OFFICE ELECTRONIC CONTROL FOR GRAVIMETRIC FEEDERS George Kast, Homer City, Pa., assignor to Syntron Company, Homer City, Pa., a corporation of Delaware Application November 30, 1949, Serial No. 130,317

3 Claims. 1

beam balance will result in a phase reversal of 180 from one side of the balance point to the other. Such a change is proportional to the displacement of the iron core relative to the balance point. The phase angle may vary Within a small range of movement of the beam from the in phase position to 180 out of phase position or lagging with respect to the plate voltage. Since the amount of current passed tory feeder is automatically controlled by the by the thyratron to the vibratory conveyor is a load on the scale-suspended constant speed confunction on the phase of its grid voltage, with veyor belt. Any variation of the weight or load respect to its anode voltage, the current passed on the belt conveyor varies the current supplied by the thyratron will be a function of the position to the vibratory feeder which in turn corrects of the iron core in the inductive transducer actuthe amount of material supplied to the constant ated by the Weighing device with respect to the speed belt and thus maintains an accurate feed iron core in the other inductive transducer that of continuously flowing material. is manually positioned to provide a correct feed The object of this invention is the provision of material. of a new and improved control circuit for the The degree of sensitivity of the system may be vibratory conveyor of a gravimetrie feeder. changed by varying the mechanical ratio be- These vibratory conveyors are preferably optween the scale deflection and transducer core erated on pulsating current obtained from a movement. By this means, the feeding charrectified alternating current. In this invention acteristic of the vibratory feeder can be changed the rectified current pulsations are obtained from a practically steady flow, with gradual corfrom atriode, such as agrid controlled thyratron, rection, to a cyclically varying flow of over rate the control grid of which is fed from a bridge of feed and under rate of feed to result in a very circuit made up of two inductive transducers, exaccurate average of th material supplied. cited by the alternating current supply and Another object of this invention resides in the varied by the weight of the material on the simplicity of this control circuit and the relaconstant speed conveyor belt. tively few number of elements required to per- This bridge control circuit employs one of the form an improved and more accurate control for inductive transducers as the manual means to the gravimetrie feeder. set the desired rate of flow which, manual means Other objects and advantages appear hereinmay be remote of the gravimetric feeder. after in the following description and claims.

Any variation in weight of the material on the The accompanying drawings show, for the purconstant speed conveyor or from the selected pose of exemplification without limiting the weight of material causes the beam to move the claims thereto, certain practical embodiments core of one of the inductive transducers, which of this invention wherein the View shown is a electrically varies the bridge circuit and shifts schematic diagram illustrating the electronic the phase of the voltage in the output circuit control circuit comprising this invention whereto the control grid of the thyratron with respect in: to the anode voltage. This control circuit thus Fig. l is a complete circuit diagram of the functions to shift the phase of the control grid feeder control circuit with the thyratron directly voltage to the thyratron which changes the magsupplying the operating current for the feeder; nitude of the current supplied to the vibratory and conveyor. This increases or decreases the flow Fig. 2 is a partial circuit diagram showing the of material per unit of time from thevibratory thyratron functioning. conveyor to the constant speed conveyor for the Referring to the drawing, one side of the alterpurpose of correcting any weight inaccuracy dehating current supply is connected by the line I tected by the weighing device. The variation in D0 to one end of the electromagnetic motor 2 of the the phase relation of the grid voltage to the plate voltage is extremely great near the balance point of the bridge circuit. In other words, a small movement of the iron core in the inductive transducer produced by the movement of the vibratory conveyor 3 suspended in the air by the lines l. The top of the vibratory conveyor 3 is arranged to receive material from a suitable source such as a hopper, not shown, and supply the same to the synchronous belt conveyor 5 that is suspended by means of the members 6 from the weighing scale platform I. The weighing scale is provided with the dial 8 and the poise balance arm 9, one end of which is arranged to operate the inductive type transducer Ill by moving the iron core ll longitudinally therein, the core ll being connected to the end of the beam 9 by means of the link [2.

The other inductive type transducer 13 is also provided with a magnetic core l4 having attached at one end the rack member l which is engaged by the gear member l6 that may be rotated manually by the handle I] which has an indicator l8 thereon for the purpose of visually indicating the amount of material to be fed per unit of time on the scale l9.

Each of the inductive transducers l0 and i3 has two windings or they may be represented as a single winding with a center tap. However, as shown, the windings and 2| of the transducer 0 are connected in the bridge circuit with the windings 22 and 23 of the transducer 13. The corresponding ends of the coils 20 and 22 ar connected by the conductor 24 and the corresponding ends of the coils 21 and 23 are connected by the conductor 25, thus completin the bridge circuit. The adjacent ends of the coils 2E and 2| are connected together and the adjacent ends of the coils 22 and 23 are likewise connected together or this point of common connection may be considered a center tap of a single winding as previously stated.

The conductors 24 and 25 are likewise connected to the opposite ends of the secondary 26 of the exciting transformer 21, the primary 28 of which is connected to the alternating current supply as indicated by the conductors l and 3G.

The alternatin current supply is connected by the conductor I to one side of the coil 2 and the other side of the coil 2 is connected by the conductor 31 to the anode 32 of the thyratron 33. The cathode 35 of the thyratron 33 is connected to the other side of the A. C. supply line by the conductor 36. The conductor also is connected to the midpoint between windings 22 and 23 of the transducer 53'.

The midpoint of the coils 25 and 2| is connected by the conductor 35 to the resistance 36 and the conductor 31 to the grid 38 of the thyratron 33. The resistor 36 merely limits the current flowing in the grid circuit.

When the knob I? is manually adjusted to position the core H3 in the transducer 13 at a selected position to provide a specific feed by the gravimetric feeder, the bridge circuit will require the iron core I i of the transducer Hi to be positioned to a certain point to result in a balance condition of the system; that is, for the magnitude of the current through the electromagnetic motor 2 to be of the value required to maintain the specific rate of feed to the synchronous belt conveyor 5'.

Since the iron core I! is positioned by the movement of the beam 9, whose movement is proportional to the rate of materia1 discharge from the vibratory conveyor 3, the position of core'll will therefore be determined by the rate of feed from the vibratory conveyor 3. The output of the bridge circuit in conductors 3G and 35'will control the operation of electromagnetic motor 2 of the vibratory conveyor 3 and thus supply: material at a given rate to the synchronous conveyor 5 which delivers the material to a discharge member M. If the material fed to the synchronous operating belt conveyor 5 is under or over the rate which will keep the system balanced as determined by the position of core l 1 relative to the set position of core [4, the rate of feed from the vibratory conveyor 3 will be automatically increased or decreased to cause the scale beam 9 to position core I! to such a point where a balance of the system will be maintained.

Thus, the voltage on the grid 33 may shift in phase relative to the voltage on the plate 32, and this phase relationship will control the magnitude of the current passed by the grid controlled rectifier 33, and thus control the operation of the electromagnetic motor 2 of the vibratory conveyor 3.

Since the iron core ll of the transducer It is free to follow the beam 9 of the scale 8 and the magnetic core M of the transducer i3 is positioned manually by some'means such as a rack and pinion controlled by the knob, the phase of the outputvoltage of the grid circuit will be a function of the relative positions of these iron cores H and M. The variation in phase is extremely gr'ea't near the point of balance of the bridge; that is, a small movement of the beam about the balance position will cause a phase reversal of from one side of the electrical balance point to the other, thereby providing a quick and positive control through the grid voltage in the operation of the thyratron and thus' controlling the operation of the electromagnetic motor 2 of the vibratory conveyor 3.

Since the amount of the current passed by the thyratron 33 is a function of the phase of the grid voltage with respect to the anode voltage, the current passed by the thyratron will be a function of the position of the core H with respect to the core I4 in the inductive transducers l0 and I3, respectively. If the phase of the grid voltage is made to vary from in-phase to 180 lagging with respect to the anode voltage, corresponding to the movement of the scale beam 9 from an underweight to an overweight about a selected point on the scale, then likewise the output of the vibratory conveyor 3 will be increased if the scale is underweight and will be, decreased if the scale is overweight. Because of this characteristic, this circuit provides a means for selecting a desired rate of feed merely by adjusting the position of the iron core l of the transducer 13. The current through the electromagnetic motor} of the vibratory conveyor 3' will automatically adjust itself to the correct value to maintain the desired rate of feed of material to the synchronous conveyor 5.

Should the change in density of the material being fed, or some other condition result in a new current requirement to maintain the specific rate of feed, then, within a small movement or" the beam, the new current magnitude will automatically be obtained, which will again result in a balance of the system and a constant rate of feed from the gravimetric feeder.

In Fig 2, the electromagnetic motor 2 of the vibratory feeder conveyor 3 is operated by alterhating current supplieddirectly from the line and the current is controlled by the saturable reactor d2 having two windings and l lon a single core. The winding 13- is connected in series with the motor 2 across the source of alternating current supply designated-by I and 3 9 The winding 4'4 is connected from the plate 32 to the alternating current supply line i and has a rectifier, such as the dry disc rectifier 45 connected in multiple therewith. The low resistance path to the flow of current of the rectifier 45 is in the direction from the plate 32 to the line I.

Variation of the current to the motor 2 will result from an impedance change of the saturable reactor 42 produced by flux saturation of its iron core in accordance with the control voltage of the transducer bridge circuit.

The magnitude of the current flowing through the control coil is a function of the relative positions of the transducer cores. The direct current component of the controlled rectified current is utilized to magnetically saturate the saturable reactor core. The use of the back rectifier 45 sustains the control current flowing during the negative half of the alternating current cycle and thereby results in a higher average direct current flow than would be obtained without it. The flux saturation varies in accordance with the variation of the direct current flowing through thewinding 44 and the impedance of the winding 43 varies proportionately to the flux saturation of the core. Thus, a control of the impedance of the winding 43 determines the magnitude of the alternating current flowing through the motor 2 as a function of the weight of material on the weighing device and the same automatic control will prevail.

I claim:

1. A control circuit for a gravimetric feeder having a vibratory conveyor supplying a constant speed conveyor mounted on a weighing device comprising a motor for said vibratory conveyor, a pair of inductive transducers having coils and movable magnetic cores, said coils being connected in multiple with each other and with a circuit for supplying an alternating current excitation thereto, one of said magnetic cores connected to a movable member of said weighing device and the other connected to a manually positioning member, a triode having its anode and cathode connected in series'with the motor of the vibratory conveyor, and connections intermediate said coils to form an output bridge connected to the grid and cathode of the triode to control the operation of said motor.

2. A control circuit for a gravimetric feeder having a vibratory conveyor supplying a constant speed conveyor mounted on a weighing device, comprising a motor for said vibratory conveyor, a pair of inductive transducers having coils with movable magnetic cores, said coils being connected in multiple with each other and with a secondary circuit of a transformer for supplying an alternating excitation current thereto, one of said magnetic cores connected to a movable part on said weighing device and the other being manually'adjustable to a selected position corresponding to a desired weight of material to be fed per unit of time, a triode having its anode and cathode connected in series with the motor of the vibratory conveyor, and connections intermediate said coils to form an output bridge circuit, the coil connection from the manually operated transducer being connected to said cathode and the other coil connection being made through a resistor to the grid of said triode to change the operation of said motor upon weight changes eifective in the movement of the core connected to the weighing device.

3. A control circuit for a gravimetric feeder having a vibratory conveyor supplying a constant speed conveyor mounted on a weighing device comprising a motor for said vibratory conveyor, a pair of inductive transducers having coils and movable magnetic cores, said coils being connected in multiple with each other and with a circuit for supplying an alternating current excitation thereto, one of said magnetic cores connected to a movable member of said weighing device and the other connected to a manually positioning member, a saturable reactor having two windings on a core, a thyratron having its anode and cathode connected in series with one of the windings of said reactor and across an alternating current supply, a connection placing the other winding of said reactor in series with the motor of the vibratory conveyor and across the alternating current supply, and connections intermediate said coils to form an output bridge circuit connected to the grid and cathode of the thyratron to control the operation of said motor.

GEORGE KAST.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,276,383 Francis Mar. 17, 1942 2,366,415 Lindsay Jan. 2, 1945 

